The vtkCellArray does seem like the most likely issue, a summary of its changes for VTK 9 are described in the following thread:
https://discourse.vtk.org/t/upcoming-changes-to-vtkcellarray
The vtkCellArray does seem like the most likely issue, a summary of its changes for VTK 9 are described in the following thread:
https://discourse.vtk.org/t/upcoming-changes-to-vtkcellarray